1. Field of the Invention
This invention relates to a two circuit evaporator system of increased refrigeration capacity and increased dehumidification capacity, especially when one circuit is inactive, for use with any two circuit air conditioner, refrigeration or heat pump system. This invention more particularly pertains to an apparatus and method comprising a two circuit evaporator system that allows for integration of the two circuits in such a way as to eliminate any possibility of any portion of the air passing through the face of the evaporator, when one circuit is inactive, not coming into contact with some portion of the active circuit. Further, this invention incorporates the principles of increasingly colder refrigerant temperatures counter flow to the direction of the incoming air supply as illustrated in U.S. Pat. No. 6,116,048, the disclosure of which is incorporated by reference herein.
2. Description of the Background Art
Presently, there exist many types of devices designed to operate in the thermal transfer cycle. The vapor-compression refrigeration cycle is the pattern for the great majority of commercially available refrigeration systems. This thermal transfer cycle is customarily accomplished by a compressor, condenser, throttling device and evaporator connected in serial fluid communication with one another. The system is charged with refrigerant, which circulates through each of the components. More particularly, the refrigerant of the system circulates through each of the components to remove heat from the evaporator and transfer the heat to the condenser. The compressor compresses the refrigerant from a low-pressure superheated vapor state to a high pressure superheated vapor thereby increasing the temperature, enthalpy and pressure of the refrigerant. A superheated vapor is a vapor that has been heated above its boiling point temperature. It then leaves the compressor and enters the condenser as a vapor at some elevated pressure where the refrigerant is condensed as a result of heat transfer to cooling water and/or ambient air. The refrigerant then flows through the condenser condensing the refrigerant at a substantially constant pressure to a saturated-liquid state. The refrigerant then leaves the condenser as a high pressure liquid. The pressure of the liquid is decreased as it flows through the expansion valve causing the refrigerant to change to a mixed liquid-vapor state. The remaining liquid, now at low pressure, is vaporized in the evaporator as a result of heat transfer from the refrigerated space. This vapor then enters the compressor to complete the cycle. The ideal cycle and hardware schematic for vapor-compression cycle refrigeration is shown in FIG. 1 as cycle 1-2-3-4-1. More particularly, the process representation in FIG. 1 is represented by a pressure-enthalpy diagram, which illustrates the particular thermodynamic characteristics of a typical refrigerant. The P-h plane is particularly useful in showing amounts of energy transfer as heat. Referring to FIG. 1, saturated vapor at low pressure enters the compressor and undergoes a reversible adiabatic compression, 1-2. Adiabatic refers to any change in which there is no gain or loss of heat. Heat is then rejected at constant pressure in process 2-3, and the working fluid is then evaporated at constant pressure, process 4-1, to complete the cycle. However, the actual refrigeration cycle may deviate from the ideal cycle primarily because of pressure drops associated with fluid flow and heat transfer to or from the surroundings.
It is readily apparent that the evaporator plays an important role in removing the heat from the thermal cycle. Evaporators convert a liquid to a vapor by the addition of latent heat. Latent heat is the amount of heat absorbed or evolved by one mole, or a unit mass, of a substance during a change of state such as vaporization at constant temperature and pressure. Most commercially available evaporators have a coil of a tubular body extending within the evaporator for the purpose of providing a heat exchange surface. In a two circuit evaporator, the coils of such evaporators are currently one of two primary types, both with serpentine rows of tubing extending through the evaporators with currently no apparent concern about refrigerant temperature being colder counter flow to the incoming direction of the air supply. Type one is the split face coil design in which one circuit occupies a percentage based on percentage of total capacity for the circuit, of the overall face area of the evaporator, and the other circuit occupying the remaining percentage of the overall face area. When one circuit is inactive, the air passing through the inactive circuit acts like bypass air and no cooling to this fraction of the circulated air is accomplished and the blower motor power for this portion of the air supply is virtually wasted.
The second type of two circuit evaporator is known as an alternating circuit evaporator where each circuit has multiple inlet and outlet points that alternate with multiple inlet and outlet points of the other circuit. This is more efficient and effective than the split face evaporator but still produces a bypass air effect one each of the alternating portions of an inactive circuit.
By integrating the alternating circuits, the bypass air effect can be minimized if not totally eliminated. Coupled with the principle of counter flow heat exchange as illustrated by U.S. Pat. No. 6,116,048, the effectiveness in capacity per evaporator surface area and dehumidification improvements will be greatly enhanced for two circuit evaporators versus any of the known embodiments of the evaporator art.
In response to those realized inadequacies of earlier configurations of two circuit evaporators used within the thermal transfer cycle of two circuit air conditioner, refrigeration equipment and heat pumps, and their resulting inefficiencies, it became clear that there is a need for integrated counter flow dual circuit evaporator designs that would take advantage of the known benefits of fluid to fluid counter flow heat exchange and the known benefits of elimination of bypass air. The results of the use of these new evaporator designs being greater refrigeration capacity and improved dehumidification, especially in part load application where one circuit is inactive, where the benefits are realized at no additional power consumption for the total refrigeration thermal cycle.
The greater capacity being realized from the higher mass flow of refrigerant through the evaporator is due to improved heat exchange brought about by elimination of the bypass air regions as well as counter flow principles and greater dehumidification brought about by the entire coil being colder than the dew point temperature because of the same reasons as above. Inasmuch as the art consists of various types of two circuit evaporators and associated thermal transfer cycle configurations, it can be appreciated that there is a continuing need for and interest in improvements to two circuit evaporators and their configurations, and in this respect, the present invention addresses these needs and interests.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the two circuit evaporator art.
Another object of this invention is to provide new and improved integrated dual circuit evaporator which has all the advantages and none of the disadvantages of the earlier two circuit evaporators in a thermal transfer cycle.
Still another objective of the present invention is improved thermodynamic efficiency.
Yet another objective of the present invention is to provide elements of circuit integration and counter flow principles to all possible variations of types and purposes of evaporators, including those with minimum sub-cooling, maximum sub-cooling, minimal superheat, maximum superheat, low pressure gradients, high pressure gradients, low “glide” temperature spreads, high “glide” temperatures spreads, as well as for: flat coils, slant coils or “A” coils, and for: down-flow or up-flow designs. The purpose for each design being to eliminate bypass air when one circuit of a two circuit evaporator is inactive and to put the warmest part(s) of the evaporator upstream in the air flow from the coldest part(s) of the evaporator.
Still a further objective of the present invention is to provide increased refrigeration capacity.
Yet a further objective is to allow for increased latent heat removal and, therefore, increased dehumidification.
An additional objective is to provide an evaporator that is highly reliable in use.
Another objective of the invention is to provide an evaporation system having an increased energy efficiency ratio (EER) as a result of a decrease in wattage input and an increase in refrigeration capacity.
Even yet another objective of the invention is to provide two circuit evaporators where the two circuits are integrated to prevent bypass air when one circuit is inactive and where both circuits comprise in combination two or more sections of each evaporator circuit positioned in the air stream so that the warmest section(s) of each evaporator circuit is (are) upstream of the coldest section(s) of each evaporator circuit is pre-cooled before coming into contact with the colder downstream section(s) of e4ach evaporator circuit.
Another objective of the present invention is to provide a method for enhancing latent heat removal in a thermal transfer cycle by cooling the air to temperatures even lower than standard evaporators so that the air is substantially below the dew point temperature of the air. By increasing the temperature difference below the dew point temperature, more humidity is removed and the latent capacity percentage of the total heat removal is increased.
Yet another objective of the present invention is to provide a method for increasing the superheat capacity of a refrigerant in a thermal transfer cycle. This increases the total change in enthalpy of the refrigerant per unit mass flow and thereby increases overall capacity. This is accomplished by putting the warmer superheat region of the evaporator upstream in the air supply from the colder region(s) thereby supplying more heat to this superheat region.
Even yet another objective of the present invention is to provide an apparatus and method that will increase overall refrigerant mass flow thereby increasing refrigerant capacity while doing so in a more efficient manner.
And yet another objective of the present invention is to provide a method and apparatus that will improve the load performance of a two circuit evaporator when one circuit is inactive, whereby capacity, dehumidification, and mass flow are all greatly improved.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.